1. Field of the Invention
The present invention relates to a zoom lens, and is suitable for an imaging optical system used for an image-pickup apparatus such as a digital still camera, a video camera, a monitoring camera, a broadcast camera, and a film-based capturing camera.
2. Description of the Related Art
Since an imaging optical system for an image-pickup apparatus is required for a short lens overall length, a small overall system, and a zoom lens having a high zoom ratio. It is also required for a high optical performance in the entire zoom range and over the whole object distance.
There is known a four-unit zoom lens that includes, in order from an object side to an image side, a first lens unit of a positive refractive power, a second lens unit of a negative refractive power, a third lens unit of a positive refractive power, and a fourth lens unit of a positive refractive power.
U.S. Pat. No. 5,260,834 discloses a small zoom lens in which a second lens unit and a third lens unit are configured to move in zooming.
Japanese Patent Laid-Open No. (“JP”) 2000-330016 discloses a zoom lens having a zoom ratio of about 10 in which each lens unit is configured to move in zooming.
It is important for these four-unit zoom lenses to appropriately set a lens configuration of a third lens unit particularly among lens configurations of each lens unit, and a moving amount of the third lens in zooming for a high zoom ratio and a small overall system.